[Day27] Read Rust Atomics and Locks - Something to know about memory ordering

by Mara Bos

At Topic: Chapter 3. Memory Ordering, Common Misconceptions

Notes

Memory ordering is about things like reordering instructions, which usually happen at nanosecond scale no matter which ordering is used.
Even if we disable compiler optimization, we should still care about memory ordering.
Even if we use processors having only one core and only ever executing one instruction at a time, all in order, we should still care about memory ordering.
On all modern platforms, relaxed load and store operations compile down to the same processor instructions as non-atomic reads and writes.
Compilers tend to avoid most types of optimizations for atomic variables.
If any other memory ordering is correct, SeqCst is also correct. However, it’s possible that a concurrent algorithm is simply incorrect, regardless of memory ordering.
When seeing Release, it means "this relates to an acquire operation on the same variable"
When seeing SeqCst, it means "this operation depends on the total order of every single SeqCst operation in the program"
When Seeing SeqCst, two things should come to mind:
1. something complicated is going on
2. The author might not take the time to analyze the memory ordering
A "acquire-store" or "release-load" are not possible
A Release-store does not form any release-acquire relationship with a SeqCst-store.